User identification devices have become increasingly popular for decreasing security threats, increasing safeguard techniques, and to help prevent fraud. Typically, a user identification device is used to gain access to a location or a system or may be used simply for identification, such as gaining access to your personal electronic device. One type of conventional user identification device is a biometric sensor in fingerprinting. Fingerprints have been widely accepted as unique identifiers for individuals. That is no two people have been known to have the exact fingerprint. Conventional fingerprint sensors typically require a user to place a finger or hand on the sensor. The fingerprint is detected by the sensor, and compared to a catalogued fingerprint for the user.
One type of conventional fingerprint sensor is a capacitive fingerprint sensor. A fingerprint is comprised of ridges and valleys. When a finger is placed on the sensor a capacitance is measured. The measured capacitance varies per user because each user has different ridges and valleys on their respective fingers.
Capacitive fingerprint sensors are popular but may be inaccurate due to the inability to make fine-grain measurements. For example, a conventional capacitive sensor may comprise two conductive plates and a dielectric formed there between. The capacitance changes as a result of placing a finger on one of the conductive plates. These sensors may be inaccurate due to noise. The change in capacitance sensed by the sensors when measuring a fingerprint should be much larger than a nonsystematic error in measurement, which may be caused by changes in contact between the device and the finger, or much larger than any errors in measurement that may result from natural or seasonal drift, such as drift resulting from seasonal, environmental changes or ageing Some conventional sensors are not capable of taking fine grain-measurements for different sections of a fingerprint and thus may result in two people having indistinguishable capacitive measurements.
Furthermore, conventional fingerprint sensors are subject to spoofing. For example, a gel formed as an authorized person's fingerprint or a finger removed from a deceased person may be used by an unauthorized user to trick a fingerprint sensor and gain access to a location or a system, because conventional fingerprint sensors typically do not determine a physical attribute of the object with the fingerprint, such as whether the physical attribute is such as living or dead human tissue.